DOE OSTI2020
Ca2Sb2O7 crystallizes in the orthorhombic Imma space group. The structure is three-dimensional. there are two inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded in a distorted body-centered cubic geometry to eight O2- atoms. There are four shorter (2.46 Å) and four longer (2.74 Å) Ca–O bond lengths. In the second Ca2+ site, Ca2+ is bonded to eight O2- atoms to form distorted CaO8 hexagonal bipyramids that share corners with two equivalent CaO8 hexagonal bipyramids, corners with two equivalent SbO6 octahedra, and edges with six SbO6 octahedra. The corner-sharing octahedral tilt angles are 55°. There are a spread of Ca–O bond distances ranging from 2.27–2.83 Å. There are two inequivalent Sb5+ sites. In the first Sb5+ site, Sb5+ is bonded to six O2- atoms to form SbO6 octahedra that share corners with six SbO6 octahedra and edges with four equivalent CaO8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 44–46°. There is four shorter (1.99 Å) and two longer (2.00 Å) Sb–O bond length. In the second Sb5+ site, Sb5+ is bonded to six O2- atoms to form SbO6 octahedra that share corners with two equivalent CaO8 hexagonal bipyramids, corners with four equivalent SbO6 octahedra, and edges with two equivalent CaO8 hexagonal bipyramids. The corner-sharing octahedral tilt angles are 46°. There are two shorter (1.99 Å) and four longer (2.03 Å) Sb–O bond lengths. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to two Ca2+ and two Sb5+ atoms. In the second O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Ca2+ and two equivalent Sb5+ atoms. In the third O2- site, O2- is bonded to three Ca2+ and one Sb5+ atom to form a mixture of distorted edge and corner-sharing OCa3Sb tetrahedra.